Refer to Create your first .Net core console application on Ubuntu to understand in detail how to create your first .Net Core console application on Ubuntu.
I will assume that you already have basic understanding about Docker and have access to a machine with Docker client installed.
Create and publish .Net Core console application
Create a new console application hellodocker with below command:
dotnet new console -o hellodocker
Edit hellodocker/Program.cs and update message from Hello World! to Hello Docker!.
Verify that you are able to either run or build the application with dotnet run or dotnet build.
Now proceed with publishing the application, so that we can use the output to create Docker image.
dotnet publish --configuration Release
As we have not mentioned any specific output directory, by default the output will be available inside /bin/Release/netcoreapp2.1/publish/
Create Docker file
We will use mcr.microsoft.com/dotnet/core/runtime:2.1 as base image. This is an official Docker image with .NET Core 2.1 runtime from Microsoft.
We need to create a Docker file where we will start with a base image and then copy the published output from .Net Core console application and the provide entrypoint for the container.
Create a file named Dockerfile in directory hellodocker and put following content using your favourite editor.
FROM mcr.microsoft.com/dotnet/core/runtime:2.1
WORKDIR /app
COPY /bin/Release/netcoreapp2.1/publish/ .
ENTRYPOINT ["dotnet", "hellodocker.dll"]
Here we are copying everything inside /bin/Release/netcoreapp2.1/publish/ into Docker image and specifying the entrypoint where it will run command dotnet hellodocker.dll.
Create Docker image
Docker image can be created with below command:
docker build -t hellodocker:1.0 .
In above command, with parameter -t we have specified that we want to name docker image hellodocker and tag as 1.0.
Sample output:
Sending build context to Docker daemon 183.8 kB
Step 1/4 : FROM mcr.microsoft.com/dotnet/core/runtime:2.1
---> 6bf090c289b7
Step 2/4 : WORKDIR /app
---> Using cache
---> ef1c367ba7a9
Step 3/4 : COPY /bin/Release/netcoreapp2.1/publish/ .
---> fb8a16c17123
Removing intermediate container 9c904d1f6e06
Step 4/4 : ENTRYPOINT dotnet hellodocker.dll
---> Running in 176ba4914624
---> be9d0437b610
Removing intermediate container 176ba4914624
Successfully built be9d0437b610
You can confirm that the docker image was created with below command:
docker images hellodocker:1.0
# Output
REPOSITORY TAG IMAGE ID CREATED SIZE
hellodocker 1.0 be9d0437b610 54 seconds ago 180 MB
Run docker container
To run the docker image as a container, use below command:
docker run hellodocker:1.0 --name hellodocker
# Output
Hello Docker!
Docker container will exit immediately, because we had specified a very simple console application as entry point which prints a message on console.